Zalepon (CL-284846) is a novel, pyrazolopyrimidine, sedative-hypnotic which binds weakly but differentially to the GABA brian complex. In animal models, it produced potent sedative and anticonvulsive effects similar to marketed benzodiazepines. In tests for side effect potential, zalepon, unlike most marketed sedatives, produced no hangover effect, exhibited less propensity for memory loss, reduced tolerance, (suggesting a lower potential for abuse), and at an efficacious dose showed a reduced tendency to pontentiate depressant effects with alcohol. In addition, human pharmacokinetic data predict a fast onset and elimination. Based on the medical need ofr improved sedative-hypnotics and the results of preclinical and clinical studies thus far conducted, zalepon has the potential to be an effective treatment for the symptoms of insomnia with fewer side effects than are commonly associated with most drugs currently marketed for this purpose. The primary objective of this study is to evaluate the effects of zaleplon 10 and 20mg as compared to zolidem (AMBIEN) 10 and 20mg with regard to the time course of EEG and performance test effects. A secondary objective is to relate these effects to the plasma concentration of the specific drug therapy. This study represents a double-blind, placebo-controlled, randomized 5-period crossover design. This study will be conducted at a single investigational site using a total of 10 healthy males and/or females form 18- 45 years of age. Each subject will participate for up to 31 days, including a pre-study screening to occur within 21 days of the first study drug administration, and a 10 day (10 night) confinement period. The first aftenoon prior to the confinement period (day 1) will be used to acclimate the subjects to the study center, to familiarize, them with the performance tests to be conducted (no study drug will be administered and data will be collected) and undergo pre-test article administration tests. Starting on day 1 of the confinement peroid ( and continuing every 48 hours until they have received all five treatments), subjects will be given a dose of study medication at approximately 9 am. Each dose of the study drug will be separated by a 48-hour washout period. All subjects will undergo a final evaluation immediately following the completion of the last blood sample (day 9, hour 24). Multiple venous blood samples, EEG recordings and performance tests will be collected at specified time points. Adverse events will be monitored throughout the study, and clinical laboratory tests will be performed at specified times during the study. It is anticipated that the clinical portion of the study will be complete in 5 minutes.